1. Field of the Invention
This invention relates to valve structures for use in high vacuum systems, and more particularly to a valve structure suitable for use in ultra-high vacuum systems evacuated to a degree in the order of an eleven scale vacuum.
2. Description of the Prior Art
A preliminary patentability and novelty search has revealed the existence of the following U.S. Pat. Nos.:
______________________________________ 653,600 1,074,199 1,707,125 3,557,822 4,294,427 4,491,145 4,706,934 4,718,637 ______________________________________
Referring to the patents listed above, U.S. Pat. No. 653,600 relates to a gate valve for hydrants, and utilizes a roller acting on an inclined surface to impose a lateral pressure on the gate of the valve as the spindle moves downwardly.
U.S. Pat. No. 1,074,199 also relates to a gate valve, and this patent utilizes what might be called a "toggle" to impose a lateral pressure on the gate. In this structure, as the gate descends from an open position toward a closed position, a plate engages a corner of the housing, and continued downward movement of the gate imposes a lateral force on the gate by virtue of the lever arm formed by the plate.
U.S. Pat. No. 1,707,125 relates to a high pressure slide valve operated by a control spindle that causes rollers to move up or down in channels formed by the walls of the housing. The rollers are mounted on appropriate journals that support links the opposite ends of which are journaled on a guide block extending upwardly from a tubular member, the bottom of which is equipped with rollers that facilitate lateral translation of the tubular member when the control spindle is actuated. It thus appears that opening of the valve is dependent upon gravity and the force of a fluid pressing against the closing member.
U.S. Pat. No. 3,557,822 utilizes a toggle-type arrangement to effect lateral translation of a seal member that works in conjunction with the gate.
U.S. Pat. No. 4,294,427 utilizes cam surfaces to impose a lateral pressure on the gate valve to effect closing.
U.S. Pat. No. 4,491,145 discloses a structure wherein downward vertical movement of a spindle causes a toggle link or links to impose a lateral pressure on the seal block, while upward movement of the spindle causes the toggle links to pivot downwardly, causing the gate to move away from the orifice.
U.S. Pat. No. 4,706,934 discloses a gate valve that utilizes a wedging action to impose lateral pressure on the closure member.
Lastly, U.S. Pat. No. 4,718,637 relates to a high vacuum gate valve that utilizes a toggle system for driving the gate element into sealing engagement with the housing.
With the increase in sophistication of technology in general, there has arisen the need for greater sophistication in vacuum technology. This is particularly true in such devices as vacuum valves that are required to maintain the integrity of high and ultra-high vacuum systems. Accordingly, a primary object of the present invention is the provision of a vacuum valve device that meets the need for greater sophistication in a vacuum valve.
One phenomenon not generally known is that, within a high or ultra-high vacuum environment, metallic elements that are related in metal-to-metal physical contact tend to seize, thus preventing relative movement or rendering such movement particularly difficult. Accordingly, one of the objects of the present invention is the provision of a vacuum valve that is devoid of direct metal-to-metal contact between relatively moveable components within the vacuum valve.
Another phenomenon not generally known is that certain metals, particularly the softer metals such as copper, have an affinity for gaseous molecules that attach themselves to the surface of the metal in a thin layer that is difficult to remove. If not removed, as by simultaneous heating and vacuum pumping, such gaseous molecules are released over time and effect degradation of the vacuum environment. Accordingly, another object of the invention is the provision of a vacuum valve in which the presence of metals having an affinity for gaseous molecules is minimized.
It is not generally known that metals of various types have embedded within them gaseous molecules which, if not removed or "outgassed" by appropriate processing, migrate out of the metal toward the surface of least pressure, i.e., the high or ultra-high vacuum surface of the metal component. The effect of such release of gaseous molecules into the high or ultra-high vacuum environment is degradation of that environment over time. One of the processes by which such embedded gaseous molecules are removed or "outgassed" is to "bake" vacuum devices at high temperatures while simultaneously vacuum pumping the devices to remove free gaseous molecules from their interiors and to remove gaseous molecules freed from the metal itself by the "baking" process. A disadvantage of the "baking" process is that not all materials used in the fabrication of vacuum components are susceptible to being raised to the high temperatures necessary to effectively free the embedded gaseous molecules. It is therefore still another object of the invention to provide a vacuum valve structure fabricated from materials that are capable of withstanding the high temperatures of the "outgassing" process.
Gate valves of conventional construction frequently use carefully machined seal surfaces that slidably engage a gate component to effect sealing. In a high or ultra-high vacuum environment, such a construction is inadequate for at least two reasons. First, the seizing phenomenon becomes operative, making it impossible or very difficult to move the gate in the vacuum environment. Secondly, if sufficient tolerances are provided in the structure to minimize seizing, the effectiveness of the sealing function of the valve is adversely mitigated. Accordingly, another object of the present invention is the provision of a vacuum valve structure having a "knife" edge seal component lying in a single plane and a seal plate or pad against which the "knife" edge seal may impinge to effect a seal, said components approaching, sealingly abutting, and receding relative to the other by movement in a direction perpendicular to the plane of the "knife" edge seal component.
When a vacuum valve is connected to a vacuum chamber, or a vacuum conduit connecting two separated vacuum chambers, or interposed between a vacuum chamber and the pumping equipment for evacuating the chamber, opening of the vacuum valve is a critical transition because in most instances it allows gaseous molecules at a higher pressure to invade the interior of the vacuum valve, from whence they migrate into the environment of lesser pressure connected to the opposite port of the vacuum valve, thus causing a degradation of the lesser pressure vacuum environment. The quantity of the gaseous molecules transferred in this manner is a function of the volumetric capacity of the interior of the valve. Accordingly, a still further object of the invention is the provision of a vacuum valve structure in which the interior volumetric capacity of the valve has been minimized.
In the fabrication of vacuum valves, insufficient consideration has been given to the design of the valve structure in such a manner as to preclude the formation of pockets or voids within which gaseous molecules are sealed during the fabrication process, and which, over time, migrate into the vacuum component to effect a degradation of the vacuum environment. Accordingly, another object of the present invention is the provision of a vacuum valve structure fabricated in such a manner as to eliminate such pockets or voids within which gaseous molecules may be trapped.
Still another object of the invention is the provision of a vacuum valve in which consideration has been given to the identification of critical areas of construction subjected to inordinate amounts of stress, and the selection of materials for fabrication of components in these areas of high stress that will withstand the stresses imposed on them.
The invention possesses other objects and features of advantage, some of which, with the foregoing, will become apparent from the following description and the drawings. It is to be understood however that the invention is not limited to the embodiment illustrated and described since it may be embodied in various forms within the scope of the appended claims.